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What Is A Combi Boiler?

High-efficiency condensing "combi", or combination boilers, are very popular in homes today because they can save space and money. A combi boiler is a compact and efficient unit that provides all the heat and hot water a small home needs while saving on operating and installation costs. Combis work like both central heating boilers and hot water cylinders and are so compact they can be hung from your kitchen wall.

How Combi Boilers Work

Unlike conventional systems, combi boilers do not store domestic hot water. They heat water from the cold mains directly even as you use them. With combi boilers, you do not have a hot water cylinder, loft tank, or pipework. Combis are like standard unvented boilers but they have a second heating circuit, which is what gives you the instant hot water whenever you need it. If fed directly from the main water supply to the heat exchanger, the combi boiler can have an unlimited hot water supply as long as the boiler is firing. Combis manage to extract a larger amount of heat from the flue gases that escape from the flue system, which increases the combi's efficiency.

When Combi Boilers Make Sense

Combination boilers are sometimes preferable because they eliminate some of the requirements of conventional vented heating systems. Combi boilers don't require a hot water cylinder in the airing cupboard or the cold-water tank. They also don't require the small header cistern. All the parts of a combi are in a single unit, making it very easy to install.

Combi boilers make sense in properties where space is limited, as they don't require separate tanks for hot and cold water. If there is more than one bathroom, it is better to have storage systems. The standard combi boilers heat water in about 40 seconds. Some combis control the flow of water until it is hot enough. Storage combis can store some hot water permanently.

With a combi boiler, you'll save on hot water costs. (In fact, according to a 2005 Green Affordable Housing Coalition report, combination water and space heating systems can reduce utility costs by 15 percent or more compared to standard installation of separate furnace and water heater systems.)

Condensing Combination Boilers are condensing versions of the standard combination boiler and are more efficient, giving you the advantage of a combination boiler as well as a condensing boiler. They can replace an existing combi boiler.

Major combi boiler manufacturers include:

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